Cognitive decline with aging reduces independence, quality of life, and productivity in older individuals. While much more common than neurodegenerative diseases, such as Alzheimer's and Parkinson's, the etiology of cognitive decline remains unknown. The central hypothesis of this proposed study is that differential expression of miRNAs with age and cognitive decline negatively impacts synaptic plasticity and cognition through the regulation of protein expression. Our previous studies have identified hippocampal mRNA and protein expression changes with aging and cognitive decline utilizing Fischer 344 x Brown Norway (F1) rats cognitively stratified by Morris Water Maze testing. Interestingly, in comparisons of Adult (12 month) and Aged (26 Month) Cognitively Intact, and Aged Cognitively Impaired rats we have identified a number of changes in protein expression related to neuronal plasticity that are not regulated at the transcript level. This suggests a role for alternate mechanisms of protein expression regulation, including miRNAs. In pilot studies using the same model and behavioral testing we have identified miRNAs regulated with age and miRNAs specifically regulated between cognitively intact and impaired aged animals. The predicted targets of these miRNAs included many of those proteins that we have identified as down regulated but whose transcript levels are unchanged. This suggests a role for miRNAs as one of the regulatory mechanisms underlying the hippocampal protein expression changes with cognitive decline and aging. To expand on our preliminary results, in the first specific aim, hippocampal expression of all known rat miRNAs will be determined in CA1, CA2/3 and DG hippocampal sub regions of Adult and Aged cognitively stratified Fischer 344 x Brown Norway rats. This will provide the first genome-wide examination of hippocampal miRNA expression with aging and cognitive impairment. Differentially expressed miRNAs will be confirmed by qPCR and potential targets will be determined by in silico analysis. Following target prediction, all miRNA expression and target data will be integrated with our existing mRNA and protein expression datasets on aging and cognitive decline to identify likely points of regulation by specific miRNAs. The second specific aim will determine specific sets of proteins regulated by differentially expressed miRNAs. Specific miRNAs regulated with cognitive decline or aging will be over/under-expressed in neuron cell culture to assess both specific and global changes in protein expression. Differentiation of direct/indirect regulation will be determined through reporter assays using the 3' UTR of regulated genes. Knowing not only the miRNAs regulated with aging and cognitive decline but their confirmed regulatory targets will allow for an understanding of the potential outcome of altered miRNA expression on plasticity and cognition.